The risk factors that contribute to the development of vascular disease in diabetes are not fully defined. This proposal focuses on defining the role of plasma prekallikrein (PK) in the initiation and progression of vascular disease in type 1 diabetes, and on describing the molecular determinants of plasma PK that foster the development of diabetic vascular complications. Exciting new information has been generated by the PI from clinical, animal and basic studies on novel mechanisms and functions of plasma PK. Preliminary studies based on cross-sectional data generated from the DCCT/EDIC-cohort of type 1 diabetic patients, demonstrated an independent association between plasma PK and microalbuminuria, hypertension and elevated lipids. Multivariable regression analysis provided the first evidence of an independent and positive association between plasma PK levels and common and internal carotid intima medial thickness. A novel polymorphism (SNP) in the coding region of the plasma PK gene was identified. Survival analyses demonstrated that the onset of microalbuminuria occurs at a more rapid rate in diabetic subjects with the SNP than without the SNP. Finally, we discovered a novel mechanism of plasma PK activation by vascular smooth muscle cells (VSMC). Once activated, plasma kallikrein stimulates MAPK phosphorylation via transactivation of the epidermal growth factor receptor and induces apoptosis of VSMC. We hypothesize that, increased levels of plasma PK are a result of the diabetic state and play a pivotal role in the initiation and progression of diabetic vascular disease. To test this hypothesis, we propose the following specific aims: 1) To determine whether type 1 diabetic patients who develop renal and vascular disease have antecedent increases in the levels of plasma PK compared with type 1 diabetic patients who do not develop renal and vascular disease. 2) To determine the role of plasma prekallikrein in the initiation and progression of atherosclerosis and nephropathy in diabetic Apolipoprotein E (ApoE-/-) null mice. 3) To elucidate the cellular and molecular mechanisms underlying vascular remodeling in response to plasma prekallikrein stimulation. The proposed studies should establish plasma PK as a pathologically-important risk factor for vascular disease. Mechanistically, the proposed studies should generate significant insights into novel aspects of plasma PK signal transduction and regulation of vascular disease in diabetes. The health related significance of vascular disease and vascular disease risk in diabetes cannot be overstated. It is the leading cause of morbidity and mortality in the United States. The goals of this proposal are to elucidate risk markers and mechanisms of vascular disease that are operative in diabetes and to elucidate underlying molecular, cellular and genetic determinants of vascular complications of diabetes.